The ability to cause fast changes in temperatures, particularly between very low temperatures and room or higher temperatures, on a desired surface and at a desired location, is of practical importance in many uses. Fast temperature changes can be exploited, for instance, in the treatment of various materials, for scaling or surface curing purposes, etc.
Cold and hot surfaces are used also for medical uses. For instance, cryogenic techniques are employed to destroy malignant tissues, or for plastic surgery. One example of such a use is presented in SU 774,549, which relates to a thermal treatment of biological tissues by passing heat carriers through a cryosurgical probe. The method is said to be useful in the cryyo-surgery of the human brain. This method, however, involves passing a heat carrier through a surgical probe, its subsequent heating and repeated passage through the probe. Acetone or alcohol are used as the heat carrier. Prior to its passage through the probe the heat carrier is either cooled to -70.degree.-75.degree. C., or heated to +70.degree.-90.degree. C.
Devices of this type present severe drawbacks, inasmuch as they have long lags in temperature changes, they require cumbersome heating/cooling apparatus outside the probe, and are complicated and expensive to use.
Cryosurgical instruments having both cryocooling and heating capabilities are also known in the art. One such device and its medical use have been described by Andrew A. Gage ["Current Issues in Cryosurgery", Cryobiology 19, 219-222(1982), at pp. 220-21]. The device described therein was cooled by liquid nitrogen and electrically heated, to provide hemostasis. The electrical heating, however, by its nature is a relatively slow procedure.
Another device is described in SU 1,217,377, which exploits the expansion of gases through an orifice. However, simple expansion of gas through an orifice provides relatively slow temperature changes, and the changes in temperature are relatively mild. Thus, for instance, in the device of SU 1,217,377 it is not possible to liquefy nitrogen. Additionally, this prior art device employs helium at room temperature which, expanding from a pressure of about 300 atmospheres, will attain a heating of merely about 30.degree. C. In any case, in the single pass expansion described in this reference, liquefaction of nitrogen cannot be achieved. However, helium has an inversion temperature of about 45K, which renders it possible to employ neon or hydrogen as the second gas, as is done in this reference. The highest inversion temperature of neon is about 200K, and of hydrogen is about 180K. Accordingly, these gases cannot be used while using nitrogen as the first gas, because the temperature of liquid nitrogen is 80K, and thus the heating obtainable with neon and hydrogen is low. Additionally, neon and hydrogen may be found at an inversion temperature lower than their maximal temperature, so that no heating is obtained. However, neon is expensive and hydrogen is dangerous, and the obtainable temperatures are unsatisfactory for many uses, which accounts for the lack of success of the above-mentioned device.
Copending Israeli Patent Application No. 104506, filed Jan. 25, 1993 by the same applicant hereof, the specification of which is incorporated herein by reference, provides a method by means of which a fast and periodic change of surface temperature, even down to cryogenic range, can be created, at the desired location, in a simple and effective manner. This is achieved by creating a surface having a fast changing temperature, by providing a heat exchanger coupled to an orifice opening into a jacket which is in contact with the surface to be heated and cooled, the said jacket forming a reservoir capable of housing a fluid in contact with the surface to be heated and cooled, and providing two gas sources, each gas source being independently connected to the said heat exchanger, one source providing a first gas, which liquefies when it expands through the said orifice, and the other gas source providing a second gas, having an inversion temperature lower than the temperature obtained by the liquefaction of the first gas, and causing the exhaust gas flowing out from the said jacket, to flow through the said heat-exchanger to preheat or precool the inflowing gas, as the case may be, and further causing the said first and the said second gas alternately to flow through the said heat exchanger and orifice, to cool or to heat the said surface; means being provided for allowing and stopping the flow of each gas through the said orifice.
The selection of appropriate gases is crucial. For instance, the maximum inversion temperature of helium is 43K. Thus, even when somewhat precooled by boiling nitrogen at 77.3K, it still will warm up when undergoing Joule-Thomson expansion. Furthermore, providing a preheating or precooling of the inflowing gas is not just a matter of efficiency or saving, but is an essential part of the invention, since processes and devices employing a one-pass heating or cooling, without utilizing an exchange of heat via an appropriate heat-exchanger, will not provide sufficiently low or sufficiently high temperatures, and will result in a temperature change which is excessively slow.
Heat exchangers can be of any type, and may be, e.g., a tinned tube heat-exchanger of a porous-matrix heat-exchanger, e.g., of the type described in British Patent No. 1,422,445. The device described in this British patent provides only for the cryocooling of the probe, the purpose being to maintain the temperature of the probe below -80.degree. C., thus avoiding altogether the need for heating the probe. It should be mentioned that, according to the teachings of this patent, heating was necessary, when operating at temperatures above -80.degree. C., for the purpose to prevent the probe from sticking to the tissue. However, when operating according to IL 104506, with fast cooling-heating cycles, the heat exchanger can be utilized also for heating purposes.
The first gas is preferably selected from the group consisting essentially of argon, nitrogen, air, krypton, CF.sub.4, xenon and N.sub.2 O, and the second gas is helium.
Cryogenic liquefaction occurs at the tip of the cold extremity of the device operating according to IL 104506, under the cooled metal surface. The Linde-Hampson method is applied, using the Joule-Thomson effect for cooldown to liquefaction.
IL 104506 also describes an apparatus for the cryocooling and the heating of surfaces, comprising:
1) a heat exchanger coupled to an orifice, the said orifice opening into a jacket;
2) a jacket which is in contact with the surface to be heated and cooled, the said jacket forming a reservoir capable of housing a fluid in contact with the surface to be heated and cooled;
3) two pressurized gas sources, each gas source being independently connected to the said heat exchanger;
4) means for allowing and stopping the flow of each gas through the said orifice.
The method of IL 104506 makes it possible to obtain a high frequency of temperature change. Thus, for instance, one may which, for a given application, to oscillate between temperatures of -50.degree. C. and +100.degree. C. only.